1. Field of the Invention
The invention relates to a catalyst and methods for fabricating the same, and more particularly to a photo-energy transformation catalyst and methods for fabricating the same.
2. Description of the Related Art
Exhaustion of fossil fuel resources is approaching. Use of fossil fuels is known to cause serious pollution and environmental destruction. Therefore, a clean energy source, such as wind power, biomass energy, and solar energy, which does not generate harmful waste, is required. Thus, alternative energy sources have been proposed to reduce dependence on fossil fuels and curb pollution.
Among the alternative energy sources, solar energy is already in widespread use. Technology for harnessing solar energy has been in development in hopes of establishing a clean, safe, and non-depleting power source. Solar power technologies can be classified as either solar thermal energy or solar light energy. Particularly, solar energy has generally relied upon the direct conversion of photonic energy to electrical energy through the use of photovoltaic cells, i.e. solar cells.
The conversion efficiency of solar cells depends on the semiconductor materials employed thereby. The semiconductor materials of solar cells can be classified as silicon, inorganic compound, and organic semiconductor materials. The silicon wafer-based solar cells have superior conversion efficiency (about 25%), but have the disadvantages of being expensive, having a large volume and having resource deficiencies.
In order to solve the aforementioned problems, film semiconductor solar cells have been developed and are the main type of solar cells used in solar technology. Examples of film semiconductor solar cell materials include: Cu(InGa)Se2 (CIGS), CdTe and amorphous hydrogenated silicon (disclosed by the NREL group), wherein the thin-film CIGS solar cell has superior conversion efficiency.
To efficiently convert the entire spectrum of sunlight to electrical energy, light-absorbing layers having different band gap energies should be arranged in a multilayered structure. In this manner, a cell termed a “tandem cell” can be fabricated by continuously or discontinuously varying the compositions of light-absorbing layers. It is known that the theoretical energy conversion efficiency of lamination having more than two light-absorbing layers (having different band gap energies) can be more than 40%.
AgInS2 has a band gap energy of between 1.87˜2.03 eV and AgIn5S8 has a band gap energy of between 1.80 eV˜1.90 eV, that are suitable for matching the band gap energy of CIGS (1.0˜1.7 eV), thereby promoting the conversion efficiency of solar cells.
JP6263442 discloses a method for producing AgInS2 by mixing powdery silver sulfide with powdery indium sulfide to form a colloid, then coating the colloid on substrate, and subjecting the coating to a thermal treatment. However, it is difficult to control the uniformity and adhesion of the obtained AgInS2 film. Further, JP5234894 disclose a method for producing AgInS2 film by sputtering. However, since sputtering vacuum equipment is expensive, the high costs limit mass production of AgInS2 film.
Therefore, the invention provides a method for preparing AgInS2/AgIn5S8 with high quality and low cost. Further, the method of the invention can prepare compounds with specific ratio between Ag, In, and S. Either AgInS2 or AgIn5S8 film is suitable material for thin film solar cells. Since the hybrid combination of AgInS2/AgIn5S8 has valance band and conduction band suitable for water decomposition, the hybrid combination of AgInS2/AgIn5S8 can be applied to produce hydrogen gas by water splitting or to produce C1 fuel from carbon dioxide.